This invention relates to a liquid nitrogen capillary action heat exchanger that is particularly well suited for use in refrigerated transportation storage containers.
Refrigerated trucks and other refrigerated transportation containers typically use conventional refrigerating systems operated by diesel engines. In such systems, a compressor operated by the diesel engine compresses gaseous freon or like refrigerant until it is transformed into a liquid. The pressure on-the liquid is then released through an expansion valve, and the refrigerant is passed through a heat exchanger in the refrigerated container. The liquid vaporizes in the heat exchanger, and this absorbs heat and chills the heat exchanger coils, cooling the container.
While this system is used widely, there are a number of drawbacks with the system. Diesel engines are noisy and dirty and require fuel and need repairs from time to time. They also produce undesirable gaseous emissions. The refrigerating units themselves typically use freon, which also is an undesirable pollutant when released to the atmosphere, which occasionally occurs.
Other refrigerants and processes have been used for refrigeration systems. Liquid nitrogen is one such refrigerant. Liquid nitrogen vaporizes at a much lower temperature than freon and thus provides a much colder refrigerant than conventional freon when released through a heat exchanger. Liquid nitrogen is available in pressurized containers and can be released through a heat exchanger and then to the atmosphere. Since nitrogen is the major component of air, the release of nitrogen poses no pollution threat.
Notwithstanding the advantages of nitrogen, there is considerable difficulty in handling and utilizing nitrogen in a refrigeration system. Since the vaporization temperature of nitrogen is much lower than conventional refrigerants, nitrogen flashes into gaseous form very rapidly and produces great pressure at normal atmospheric temperatures. The cooling thus occurs all at once, which is inefficient, and the pressure cannot be handled by a conventional heat exchanger.
It is an object of the present invention to provide a liquid nitrogen refrigeration system having improved and controlled cooling characteristics.